Wine 4.0 RC4 continues the polishing effort to make sure it has a nice full flavour ready for the final 4.0 release due next month.
Not quite the corker that previous releases have been, since they're not focusing on any new features right now. This latest release candidate only stated ten bug fixes and some of them are older bugs only now being noted as fixed. While it's not exactly exciting, it's good to have a clean-up of open bug reports so they know what to focus on for the next development cycle.
Comparing Wine 4.0 with the previous stable Wine 3.0 release, there's a lot of exciting changes ahead for those who don't test out the development versions. These features include: support for HID gamepads, Vulkan support, OpenGL core contexts enabled by default in Direct 3D, support for fetching BIOS information on Linux, subpixel font rendering support and much more.
Hopefully with the next development cycle once Wine 4.0 is out, they can pull in some changes from Steam Play's Proton and perhaps get Proton updated to Wine 4.0.
See the official release announcement here.